Telephone terminal equipment



Sept. 2l, 1954 K. N. BERGAN TELEPHONE TERMINAL EQUIPMENT Filed Nov. 17. 1949 4 Sheets-Sheet l i. invul' Slept. 2l, 1954 K. N. BERGAN 2,689,882

TELEPHONE TERMINAL EQUIPMENT Filed Nov. 17. 1949 4 Sheets-Sheet 2 INVENTOR. KENNETH N. BERGAN ATTY.

sept. 21, 1954 K. N. BERGAN TELEPHONE TERMINAL EQUIPMENT Filed Nov. 17, 1949 4 Sheets-Sheet 3 laoV-L '23# '0 wllgss REG g zo RING i o OUTPUT i soURcE lo? I oTRANS. |21 |08 =y INPUT i r 15 lalvg h U5 l2 i *VWM +B I \03 IIS "3 i |02 I 8 B gn-[l-TRANS B+ `|25 L +B I lol REC' B+ E REacoNTRol.

0 SEGTUUN INVENTOR.

KEN N ETH N. BERGAN ATT Y.

Sept. 21, 1954 K, N, BERGAN 2,689,882

TELEPHONE TERMINAL EQUIPMENT |5l\\ Rec. Ouipui F\G. 5 |63 i-- g 3%?. uw

4 [if l l -f- -offrssf- R t I we 2m I 'Ring Source i T i ma I l i Sprgs. 2 l I |65 Q i Z|62 J o' Rec INVENTOR.

KENNETH N. BERGAN ATTY.

Patented Sept. 21, 1954 lTELEPHONE TERMINAL lEQUIPMENT Kenneth N. Bergan, Franklin Park, Ill., assignor to Motorola, Inc., Chicago, Ill., a corporation of Illinois Application November 17, 1949, Serial No. 127,815

18 Claims. (Cl. 179-15.5)

This invention relates generally to communication systems and more particularly to a multiplex communication sys-:em in which a plurality of communications take place simultaneously over a single channel.

Multiplex communication systems have been used both for wire and radio communication in which a plurality of signals are simultaneously transmitted over a single channel. To prevent interference of the various signals, means'are provided for dividing the channel so that the various signals may thereby be separated. In one such system the channel space is divided into a plurality of frequency bands for theindividual signals. This application relates to a system of this type, which is generally designated a frequency division multiplex system. In this system subcarrier waves are modulated by the separate signals so that the signals may be individually recovered.

In the use of the channels of 4multiplex systems in telephone systems, difliculty results from the fact that direct currents which are normally used for providing controls in telephone systems are not easily transmitted. For example, it may be desirable to use a channel of a multiplex radio communication system to provide party line or dial telephone service. A party line system may be particularly applicable in a radio relay system having a plurality of ,stations as, by use of a party line, a single channel can provide a complete communication system interconnecting the various stations. it may also be desirable to interconnect various stations in the relay system to a standard dial telephone system. In such systems it is necessary to transmit signals for signalling and automatic switching in addition to the audio signals.

It is an object of thepresent invention to provide a multiplex communication system for transmission of audio frequency signals and control signals so that the multiplex system can be used to provide the types I" service offered by standard telephone wire systems.

i further object of this invention is to provide a multiple channel radio relay system in which a single narrow channel may be used to provide a party line telephone system interconnecting the stations of the relay system.

A still further object of this invention is to provide a radio communication system which can be coupled to a standard dial telephone system so that the radio link functions as a branch ofthe dial telephone system.

A feature of this invention is the provision of a multiplex communication system including frequency modulation sub-carrier transmitters and receivers having special provisions so that a con- 2 y. trol voltage applied to the transmitter provides a frequency shift thereof which is translated in the receiver to provide a control.

Another feature of this invention is the provision of terminal units for connecting subcarrier transmitters and receivers of a multiplex communication system to telephone subsets so that party line communication may be provided therebetween.

A further feature of this invention is the provision of terminal units for connecting a dial telephone switchboard and a dial telephone substation to the subcarrier receivers and. transmitters of a multiplex communication system whereby the multiplex communication system operates as a part of the dial telephone system.

Further objects, features and advantages will be apparent from a consideration of the following description when taken in connection with the accompanying drawings in which:

Fig. l illustrates in block diagram form a complete communication system in accordance with the invention;

Fig. 2 is a circuit diagram of a subcarrier transmitter;

Fig. 3 is a circuit diagram of a subcarrier receiver;

Fig. 4 illustrates a party line terminal and telephone subset for use therewith;

Fig. 5 illustrates a terminal for connecting a dial telephone switchboard to the radio communication system; and

Fig. 6 illustrates a terminal circuit for connecting a dial telephone subset to the radio communication system.

In practicing the invention there i-s provided a multiplex radio relay communication system including a pair of terminal stations and a plurality of intermediate relay stations. This system may operate at microwave frequencies with the microwave transmitted being modulated by a plurality of subcarrier waves. Each of the subcarrier waves may be modulated by an audio wave so that a plurality of audio signals may be simultaneously transmitted. In the radio relay operation the microwave frequency may be demodulated at each relay station to provide the various subcarrier waves but the subcarrier waves will not be demodulated unless it is desired to obtain information from one of the channels at the relay station. The subcarrier transmitters are of the frequency modulation type and are designed so that a bias voltage may be applied thereto to cause a shift in the output frequency y thereof. This wide frequency shift is translated by the subcarrier receiver into a control which may be used in a number of ways which will be described. Party line terminals are provided 3 which may be connected to the subcarrier re ceivers and transmitters at the stations for providing a party line communication system between the various stations. The radio communi- 4 triode 3I as a reactance modulator, the triode 32 as an oscillator, and the triode 33 as a cathode follower output stage. Considering rst the os-cillator, the inductors 3i5nand 36 and thecapacitors cation systemrcan,y begused in af dial .telephone 5.;31,v 33, 3gy 4u nd 4I,l provide hefoslcmatoy fresystem for connecting a dial substation to a dial qqency controlling tank circuit. By selectively switchboard. A plurality Of Channels may` be including capacitors 38, 39, and 40, operation at provided in the multiplex radio relay System and various frequencies can .be provided. The intheSe Channels 1112157 be Used nzzvifOusfWaysfxfo :grductances'f:and 36 both aiect the amplitude Carrying the desired Signals 10V and the frequencyrof the oscillator and by proper Referring 110W 60 Jthe 'CiFefWingsfiH-Fig- 1 there i adjustmentthe-desired amplitude and frequency is illustrated a System ineluding"terminal'stacan bothberobtained. The reactance tube 3I tions A and B and relay Stations C and D. The changes the rea'ctance of the oscillator tank cirerminal stations include @.IniQTQvVEfl/e: nidlilefi'fo `ccuitcbecausefofthe. operation of the phase shift- I and. a miCrOWsVe delnOdllltOl ||.,..01`.C.Qn1 15 ing lnetwork including condensers 45, 116 land 4l munication `with an adjacent relay station. Each of the relay stationsrincludes two microwave -modulatorsID and two microwave demodulators I -I `so that `simultaneous two-way `'communication can `be cairiedon. Thesystem as disclosed includes a single -antenna I2, at ea'ch terminal l'station which-isfused for both transmitting-and receiving and separate antennas I3 and I4 foi` communicating -in the twoy directions from a relay station.

As previously stated the microwave transmission`V may include avvideband of frequencies so fthat the-transmitted microwave carriers may be modulated by a `plurality. of subcarrier waves each of which is-v modulated by a separate audio wave. Accordingly, subcarrier transmitters and 4receivers I5 and YI6 are required at each terminal lstation for transmitting and receiving signals e therefrom. Attheirelay stationsthe subcarrier vsignals neednot 'be selected and demodulated but Y may be retransmitted to the succeeding link so that the transmission proceeds alongthe various links of' the relay system. However, itmay be desired to provide communication with a relay station andv this may be accomplished by lpicking voff one or more vchannels at the relay station.

In thegsystem of Fig. 1 the signal transmitted on 'channel I, whichamodulates the subcarrier ktransmitter No. I and which is received onu the subcarrier receiver No.\ I, is not picked out at the relay stations` butis simply retransmitted from the microwave, demodulator of one linlr tothe microwave modulator of the next linkin the relay .system. Channel 2 is used to provide partyline 3 and fi in the multiplex system Vare retransl mitted at-the relay stations Iwithout being `de- Ymodulated. `Channel 4 is illustrated as being used for-extending a dial telephonesystem'with and resistor 48. The condenser 4'I is variable to adjust for variation in the capacity of the parsenting a capacitive reactan'ce-in parallelwith apcrtion of theoscillator-tanlr'circuit tothereby ichange-the reactance ofthe tank-circuitand` the vfrequency of oscillation. vThe magnitude ofthe plate current dependsupon the bias voltage appliedto the gridof -thegtube 3I soj that by apply- ;-ing the modulating-vvolt-age^tov -thisgridffthe amount-o 'change `of-the frequency of the-oscil- 4-lator is controlled.

The audio signalv is vapplied vto the grid of the mreact-ance tube through thel limiter tube 30 which glimitsgthepeaks ofthe signalapplied thereto. The input Vsignalv is `applied to' the limiterl grid throughA resistorfll and the output, is ,takenjrom '-the cathode-of-thelimiter tubek` 30 which isv coupled to the grid of the rea-,etance tube 3 I. through fcondenser-BI and resistor 52. Youtput of the osci1lator'32 is'appliedV through `AThe vmodulated resistorand condenser/56 tothe grid ofthe ',cathode'follower output .stage33. The oscillator output voltage is divided by resistors 51 and"58 to whichA theioscilla'tor output is appli-ed through resistor *59. ,T he transmitter output is 'derived from Ithe cathode,fof thecathode,follower-33.

" The'input -cir-cuitrtothe reactance modulator A includes an arrangement for` applying Va direct current 'biasthereto' for shiftingthe frequency vof 4the oscillator. A'direct current voltage/ap- `plied to; the input terminal is divided by resistors 60 landyIiI with the portionr appearing across re- "sistor f6 I being applied' through resistors '32 63 j andz' to-thetgiid ofithe reactancemodulator. Thevaluesof' resistance should lbe so vvselected that the yfrequency shift of the oscillatorf32 provided by' the "positive -bias applied at the-input -will be greaterMt-han the frequency shift resultving-'fromv modulation-of the signal `applied. Ap- -plicatiorr of` the bias-thereforeprovides aconmitter.

'- In=-Fig.' Sefthere is lillustrated a subcarrier receiverwhich cooperates-Y with --the 4subcarrier transmitter of iFig. 2 yto -derive modulation from the channel li subcarrier transmitter and receiver 6-5 '-/the'frequency modulated carrier wave andro-proatterminal A-beirlg eenneetedto"dialmswitchvide a control in responsev tothe-application of v--boardterminal 2il which is inY turnconnected t0 thebiaS--voltage tothevsubcarrierV transmitter of awdial-switchboard 22. f Thechannel V subcarrier eFig, 2. 'The subcarrier receiver includes a tuned transmitter and receiver atterminal B are-Goninput; circuit lilewhich iseffective to select a parl`'nected to. dial subset terminal v23 --Which isfin 70-ticular subcarrierwave. lv'-Theinputcircuit-in v turn 'connec ted to a dial subset 2d.

In Fig; 2 there is illustrated the circuit-diagram of the subcarrier `transmitter Whichin- YHcludesthetriode valves-30",` 3I,32 and-33. The `first triodef 36 functions'as an -irrputwlimiterythe cludes two double-tunedcircuits II and-`i2 coupled-by-a. resistor-NT3.' The tunedcircuits 'II and I'l-2 are each critica-llycoupledor slightly overcouw:pled-withthe' circuit 'I2 having a lowerimped- -Lancethanl ther4 circuit 11 I soI that energy isftransferred from the circuit 1| to the circuit 12. The resistor 13, in addition to providing thedesired coupling, also loads the tuned circuits to provide a substantially uniform response over the desired band. The selected signal is amplified by the pentode valve and limited by the pentode valve 16. The amplifier stage may be of a standard design which produces a high gain. The amplified signal is applied through transformer 11 to the limiter 16 which provides both plate and grid limiting.

The output from the limiter 16 is applied to a discriminator including the tuned circuit 18 and the double diode 19. The discriminator is of the Seeley-Foster type which is arranged to provide wide band pass characteristic. The desired voltage relationships in the discriminator are provided by placing the tap on the primary coil 80 of the transformer of the tuned circuit 18 approximately three-quarters of the length of the coil from the end connected to the limiter 16. This tap on the primary coil 80 is connected to the center point between condensers 8| and 82 which are bridged across the secondary coil 83. Quadrature voltages are therefore produced across the secondary 83 when the signal to which the secondary is tuned is applied. These voltages are rectified by the diodes 84 and 85 with the bias between the rectified voltages being proportional to the deviation of the applied frequency from the frequency to which the secondary 83 is tuned. This is the usual Seeley-Foster discriminator operation. The output of the discriminator is applied to triode 8S which operates as an audio amplifier with the output signal bebeing applied through the filter including resistor 81 and the condenser 88 to poteniometer 89. The variable tap on potentiometer 83 provides a volume control for the audio signal.

When the carrier is shifted by the subcarrier transmitter by the application of a bias voltage thereto, as previously described, the voltage applied to the audio amplifier 86 is not controlled by the potentiometer 8S. This is because a condenser 9| is provided in series with the potentiometer 8S so that the potentiometer is not grounded for direct current signals. The filter including resistor 81 and condenser 88 also does not operate on the direct current voltage so that it is not attenuated thereby. An additional resistor 92 is bridged from the output of the discriminator to the bottom terminal of the potentiometer 88 to further reduce the resistance of the coupling between the discriminator and the output amplifier. The signal from the discriminator resulting from the frequency shift is large and biases off the output amplifier 86. This is true when the frequency shift is keyed at a rate of the order of cycles per second as required for responding to dial pulses.

An additional triode section 95 is provided in the subcarrier receiver, which may provide a direct current control. This triode has the control grid thereof connected through resistor 95 to the output of the limiter 16 so that the grid will be biased in accordance with the carrier signal received. Accordingly when a strong carrier wave is received on the frequency to which the receiver is tuned, the triode 95 will be biased off 4but the triode 8B will be conducting. However,

i party line terminal which may be connected toV the subcarrier transmitter and receiver at any station in the multiplex system. This terminal is indicated at I1 in Fig. 1. Fig. 4 includes also the circuit of a subset suitable for use with the party line terminal. Thisterminal includes a transformer |00 and relays |8|, |02 and |03. The terminal is connected to the receiver output through contact |05 associated with the relay |0| and to the transmitter input through the contact |08 of this relay. With the relay energized, as shown, the signals from the receiver output are applied to the winding |01 of the transformer. The relay |8| also includes terminals and ||0 for applying `-l-B potential selectively to the receiver and the transmitter. When the relay is energized, as shown, the -l-B potential is applied to the receiver. When the relay |0| is deenergzed the winding |01 of the transformer |00 is connected to the potentiometer |08 and the variable tap thereon is connected to the transmitter input. `|B potenetial is applied to the transmitter through contact ||0. When the relay |0| is actuated the movable arm |2 thereof will engage the contact ||3 which is also movable so that it can move away from the contact ||4. However, contact will be made between the arm ||2 and the contact ||3 before the contacts ||3 and lili are broken. The purpose of this action will be described hereinafter.

A lockout relay |02 is provided which may be connected to the plate terminal of the triode of the subcarrier receiver illustrated in Fig. 2. While this circuit is conducting, the relay |02 will be energized and the contacts ||5 and IIB of the lockout relay |82 will be held in engagement. The relay |03 is designated the ringing relay and includes movable arms |20 and |2| for connecting the lines |28 and |29 extending to the subset |22 alternatively to the windings |23 and |24 of the transformer |00 or to a source of 20- cycle ringing current. An additional movable contact |25 is provided for controlling the operation of the ZO-cycle source.

The subset |22 is of the local battery type having a plurality of coils |30, |3| and |32 connected across the lines |28 and |29 and with the telephone transmitter |33 connected through contacts |34 of the push-to-talk switch and in series with battery |35 across the coil |3|. The receiver |38 is connected across the coil |32 in series with Vcondenser |31. For signalling the party line stations, a ringer |38 is connected in series with condenser |38 across the lines |28 and |29. A holding coil |40 is connected in series with a ringing key |4| and resistance |42 across the lines, with the contacts |43 of the push-to-talk switch being bridged across the ring key |4| and the resistor |42. For indicating when the party line is not in use, a neon bulb |45 may` be connected across the lines |28 and |20.

Considering now the operation of the party line terminal, when the system is in the normal position for receiving, the push-to-talk relay I0! will be energized by the current from the +B source. The lockout relay |02 is energized by the direct current from the control section of the subcarrier receiver. This relay applies potential to the lines so that the neon bulb |45 is lit. The receiver ring relay is energized by the current from +B through the winding of the relay |03 and through the output stage of the receiver. The signals from the receiver output will therefore be transferred through the transformer |00 to the lines |28 and |29, and will be reproduced by the re- .ceiver |36. When it is desired to transmit, the

push-to--talk switch is pressed connecting the audio: transmitterf |33 in seri-'es WithV the battery |35to the line-andcausing'operation ofthe-'pushto-'talk relay. The` push-to-talk relay-'is fdecnrgized'as'theholding coil |40^is shorted across the lines and shunts the winding ofthe-relay I'|.` This alsozextinguishesthe neon'bulb M5'. The :receiver ring relay yremains energized since itis connected to the receiverl output' through the contacts I3` andl it. Signals from "thef transmitter |33will" therefore be transferred through transformer |00 l to the potentiometer lfand applied to the-transmitter input. The transmitter Will beenergized through the contact I lt;

When it is desired to signal anotherk party.v this can' be laccornplishedby operating theringing key |4I'. In this condition the'push-to-talk relay Will be shuntedthrough the holdin'ga coil |50 andthe resistance |42. which'causes vthe push-to-talk relay `to `be deenergized. There 'is a small "voltage across the resistanceII, however, which is applied through contact |2.I of the ringingrelay |03 and .through contacts I I5 and: ||610f the lockout relay: :|02 to thev transmitter input. This pro- Videsa direct current bias to the transmitter which ,shiftsv the vfrequency thereof' in the manner previouslydescribed. The shifted frequency is effective to bias'oif the output of the receivers which operate in the'system. When the receiver output is thus biased off the ring relay |03 in the terminal is deenergized and the ZO-cycle ringing source is applied to the lines |23 andf|29 to actuate the ringer |38.

When the `party line terminal isv in receiving condition the operation of any' transmitter on the party line deenergizes :the lockout-relay so that the stationcannot transmit Thisf is accomplished'b'ecause the presence of a carrier. in the receiverbiases off the D. .C. control stage so that current through the relay |02 is interrupted. Thecontacts |.|5 and IIS will therefore opensc that the push-to-talk relay cannotbe shunted by the push-to-talk switch to apply a signal to the transmitter input. Therefore.z whenrany one station in the party line system: is transmitting the otherstations will be locked out and cannot interrupt. The neon bulb` 45 will be `extinguished when any station is transmittingA to indicate..- this condition to the operator;

Referencev is now made to Figs.v 5 and which illustrate the terminal equipment necessary. for dial telephone operation. Fig. 5 illustratesthe terminal equipment required at the switchboard and Fig. 6 illustrates theterminal equipmentlrequired` at a substation together with*l a suitable substation circuit These systems-include vhybrid coils so that transmission andk reception: can vbe provided by a single pair of wire lines. ITliese two circuits will be described together'v as theroperation thereof are closelyrinterrelated-` When it is desired to call the substation from the switchboard a ringing voltage will bev applied from the switchboard to the lines |50 Iand |51 (Fig. 5). This voltage` is applied throughxvvindings |52 and .|53 of the hybrid across'condenser |54 and is rectified by rectifier |55 to energize the ring relay` |56. The relay |56 when energized connects the transmitter inputl to the contact |51 which is connected to -l-B throughfresistor |58.

A direct current bias is thereby appliedto the' -relayv |60 at the substation (Fig. f'is d'eenergized and the'linesl I-and| 62' connected/'to the subset I 632 are connecte'cl'tofthe 2li-'cycle ringingsource. This causes'fltheringer |64v at thel subset to be energized--signallingthe operator at this sta-tion. Inl response tof-the' signal f the operator removes hisvfhandset from? its hook which operates switches. |:682and2If-69^tofconnect the handset |16 to lines-|51 and|-6-2 and" to connect the dial switch |655tov-therlines-Ifand-fIB. The switches |58 and I69f-areshownlintheclosed position assumed When the handset is removed from the hook. The dial:switch".|fcompletes the circuit through the. rela-y;vv |10 and'` t'het relay 'operates to connect the transmitter input nto the Winding |1| through Contact -|12 and1 connects the contact- |13` to +B to providefa: voltage-on thealinel I0 I yfor energizing the-.transmitter of -thehandset |16; f

The-"subcarrier transmitter at vthe substation is normallylbiasediofff. frequency by `the'volta'ge fromfl-l-B whichisv applied through resistor |14 and Athe=contact |f15ifof-relay- |10. Y When the handset |16is removed; switch |69 energizes the rela-y .|10 toconnect the transmitter input to contact y|1f2-a-nd.put thetransmitter back on frequency so fthat-=the receivers operating therewith willznot befbiased off. The vcurrent from theioutput stage of; the -r receiver will energize the relay/.|'80f'at"theswitchboard terminal to close contacts.|8:| which'shunt condenser |54, and to momentarily shorttherlinesl5Il-and I5I through the; contacts. |82,` |83 and '|841' The contacts I8| willdeenergize--relay |56sothat the transmitter input-Will' be: connected throughl contact |85 `and potentiometer IBBlto the winding |8-'Iof the hybrid coil.- The1contact't82 is moved into engagement-withthef contact;.|3`-When the relay |80 operates ytomomentarily `shortfthelines4 |50 and |5|V with-the contactsvl83-and |84 subsequently being broken as thecontact l|32 is moved further so that-theshortv acrossy the lines is removed.

This Y shorting of the lines-|50 and |5I provides a: signal` at the switchboard'.`

With the f terminal equipment inthe condition stated above, communication imay `be carried -on `betweenmthe switchboard and rthe substation throughrthe' subca-rr-iertransmitters and receivers; The transmitter at the'switchboard is connectedto-thewinding-` |01 -of the hybrid which is coupled to -windingw21-connected to the switch- .b0ard.-The receiver output is applied to the Winding---ISB-v-oftheu hybrid which is coupled throughfwinding|53;l to `.the switchboard. The hybrid includes ywindings-'|89 andA |90 connected in a-closed circuit through resistor I9! and con- This circuit-is eiective to balance out signalsinduced in the winding I8?! from the winding |88 throughfaction of the series connectedwindings |52, and |53 sothat the received signal is noty applied to the f transmitter. Similarly at the substation the receiver output is connected to thevvinding |95whichis coupled to the winding connectedI to the lines ISI and |62. Transmitted signals=areapplied from the windings-|91 tothe windingfl'll which is coupled through. potentiometer |16,` and' contact |12 to thetransmitterfinput. The-hybrid coils include windings; |-9.8.and:|90 connected` in series through resistor 200:and condenser 20| to balance out the effect of "receivedsignals coupled through thefvvindings'ISG-fand V|19'F'to the winding I1|. This =is the normalwoperation of such hybrid units. f

When it is.l `desiredfto, originateI a call from thesubstation the'handset |16 is removed from :the.'hoolistoclosefswitchesvl GBfa'nd I 69: This energizes the relay to return the subcarrier transmitter at the substation to center frequency and causes the switchboard to be signalled by operation of relay E80 in the manner previously described. The switchboard will, therefore, recognize the call by applying the dial tone. The party at the substation can then begin dialing which intermittently opens the switch 65 to interrupt the relay |10. This action alternately places the transmitter on and off frequency to provide intermittent biasing of the output circuit of the receiver causing the relay |80 in the switchboard terminal to follow the dialing operations. As previously stated, this relay operates to momentarily completely shunt the lines |50 and I5! to operate the dial switchboard equipment. The dial switchboard equipment then operates in the normal way to connect the desired party to the lines 150 and 15| for communication with the operator at the substation.

It is apparent from the above that the control provided through the subcarrier transmitters and receivers may be used to operate terminal equipment for providing both party line and dial operation. The special construction of the subcarrier transmitter so that a bias voltage may be applied thereto to provide a shift of the carrier frequency, and the special construction of the subcarrier receiver whereby this shift of the frequency biases off the audio stage, permits the required control over radio systems. By use of this equipment a narrow channel provides Voice transmission and also the control necessary for signaling and switching. The system, therefore, permits the use of a channel of a multiplex system for providing the desired telephone circuits.

Although certain embodiments of the invention which are illustrative thereof have been described, it is obvious that various changes and modifications can be made therein without departing from the intended scope of the invention as dened in the appended claims.

I claim:

l. A communication system operating over a relatively wide band of frequencies and within which a plurality of transmissions simultaneously take place comprising, transmitting means for frequency modulating a subcarrier wave by a low frequency signal wave, said transmitting means shifting the frequency of said subcarrier wave by a substantial amount in response to the application thereto of a direct current potential having a greater voltage than that of said low frequency signal wave, and receiving means for receiving said subcarrier wave, said receiving means including discriminator means, audio amplier means, and a coupling circuit therebetween, said discriminator means providing a voltage varying in accordance with the deviation of said subcarrier wave from the center frequency thereof, said coupling circuit substantially attenuating alternating currents produced Aby said discriminator means in response to modulation of said subcarrier wave by said signal wave, said coupling circuit applying the direct current voltage produced by said discriminator means in response to frequency shift of said subcarrier wave to said audio amplier means without attenuation to thereby block said audio amplifier means.

2. A communication system operating over a relatively wide band of frequencies and within which a plurality of transmissions simultaneously take place comprising, transmitting means including means for producing a subcarrier wave and means for frequency modulating the same in response to the application of a voltage thereto, said transmitting means including an input circuit for amplifying alternating current signals and for applying direct current signals directly to said modulating means to shift the frequency of said subcarrier wave, and receiving means for receiving said subcarrier wave, said receiving means including discriminator means, audio amplifier means, and a coupling circuit therebetween, said discriminator means providing a voltage varying in accordance with the deviation of said subcarrier wave from the center frequency thereof, said coupling circuit `substantially attenuating alternating currents produced by said discriminator means in response to modulation of said subcarrier wave by said alternating current signals, said coupling circuit applying the direct current voltage produced by said discriminator means in response to said frequency shift of said subcarrier wave to said audio amplifier `means without attenuation to 'thereby block said audio amplifier means.

3. A communication system operating over a relatively wide band of frequencies and within. which a plurality of transmissions simultaneously take place comprising, transmitting means for frequency modulating. a subcarrier Wave by a low frequency signal wave, said transmitting means shifting the frequency of said subcarrier Wave by a substantial amount in response to the application thereto of a direct current potential having a greater voltage than that of said low frequency signal wave, and receiving means for receiving said subcarrier wave, said receiving means demodulating said subcarrier wave to derive said alternating current signals therefrom and to provide a direct current voltage in respense to said shift of said subcarrier wave, said receiving means including an output stage which amplifies said alternating current signals and which is blocked by said direct current voltage.

4. A communication system comprising,itrans mitting means for frequency modulating a subcarrier wave in accordance with the voltage applied thereto, said transmitting means including means for amplifying alternating current signals applied thereto and for shifting the frequency of said subcarrier wave in response to the application of a direct current potential thereto, and receiving means for receiving said subcarrier wave, said receiving means demodulating said subcarrier wave to derive said alternating current signals therefrom and to provide a direct current voltage in response to said shift of said subcarrier wave, said receiving means including an output stage which ampliies said alternating current signals and which is blocked by said direct current voltage.

5. A communication system comprising, transmitting means including means for producing 'a carrier wave and means for frequency modulating the same in response to the application of a voltage thereto, said transmitting means including an input circuit having amplifying means for applying an alternating current signal wave to said modulating means and having attenuating means for applying direct current signals to said modulating means to shift the frequency of said carrier wave, and receiving means for receiving said carrier Wave, said receiving means including discriminator means, audio amplifier means, and a coupling circuit therebetween, said discriminator means providing a voltage varying in accordance withthe deviation of said carrier wave agceagsce from `the-centerfrequency-thereone said A-coupling circuit substantially attenuat-ingfalternatingicurrent `voltages Aproduced lbyn--said f discriminator means -in response1to=mo`dulation 'offsaidfcarrier wave by said signal wave,=-said1eoupling circuit applying direct ycurrentvvvoltages yproduced "by said discriminator meansciny responsefltov-said frequency shift of' said carrier waVe-to-said-audio amplifier means without lattenuation fto' thereby block Y said' audio Aamplifier means.

6. A 4party line -telephone-system operating over a radio channel'including-infcombination, a' terminalA unit `and transmttingmeans and receivingy means -coupledvito'said*terminal unit; said terminal. unit including ymeans v'-for selectively energizing said `transmitting means `land for selectively applying-an"audiorwave and a direct current signallingcpotential-tosaid' transmitting means `when saidtransmittingmeans is enerM gized, saidv transmitting mean's'including -means for producing ascarrieriwaveeand `means-fer -frequen'cy' modulatingssaidfcarrier'Wave-fbyE 'an audio wave and -for shiftin'gi-the frequency of -said carrier wave in Yresponse tothe applicationfof said direct currentA signalling potential' thereto;

said receiving means demodulating'the frequency modulated carrier lwave of a predetermined frequency received thereby to derive said :audio Wave therefrom'andto provide a direct-Voltage in response to said frequency shift offsaid carrier u wave, said receiving means 4having an output stage which amplies ithe'recovered audio wave and having a portion Which is blocked infresponse to said derived direct voltage, said receiving means having a `control'stage 'which is rendered l noneconductingwhen a signal o'f saidpredetermined frequency isreceived-thereby, said terminal unit including first 'circuit means coupled tov'said output stage which provides a signal in response to the blocking `ofsai'd output stage and second circuit means connected to said control stage which preventsenergization of said transmitting means 'when faf tsignal I=-of Isaid predetermined 'frequency isfvreceived--by said vreceiving means.

7. A dial telephone :system includingrin combination, rst-andrs'econd terminal units, ltransmitting means coupled to` said-'rs't terminalunit, and receiving meansv coupled f Lto Afsaid :second terminal unit, said V'flrstterminal unitselectively applyngan audio-'avavef'anddial pulses in the form of direct current'signalsrecurring at a frequency ofthe 'order "of "twenty cycles per second to saidtransmittingmeans,.said Atransmitting means Yincludingmeans foriproducinga a carrier wave yand means v`for frequency' modulatinglsaid carrier Wave'bysaid-audiowave-and for shifting the frequency of said carrier wave in response to said direct current"signalsy-saidreceiving means including .--discrimlnatorfmeans,

waveso 'that-said directv current "voltages bloclc said/audio amplifier means, said second: terminal unit including a lcircuit vcoupled to said-audio amplier means `*which provides a signal pulse'A in response to the blocking of said amplifier means.

-8. A telephone system including in combination, `first andf'second terminal units, transmitting means-coupled to said first terminalunit, and receivingmeans coupled tosaid second' terminal unit, said 'rst terminal unit selectively applyingan audio Wave and direct currentc'aliing signals-.to ysaid transmitting vmeanstisaid transmitting meansv including means for 1 producing a carrier -wavefand means forv frequency modulatingsaidcarrier Wave; by saidl audio wave and for shifting the frequency of said carrier wave-in Aresponsexto Asaid direct current signals, said receiving lmeans including discriminator means, audio yamplifier means, and .acoupling circuit therebetweenl said. discriminator ..means providing a voltage varyingrin accordance with thedeviation of saidcarrierfwave fromthe'center frequency `thereof, .said .discriminator voltage correspondingto said audio lfrequency vwavesf'antl to said direct current lsignals `applied tofsaid modulatingimeans, said `coup-ling circuit includingfcircuit portionsproviding aypathffor. the A audio frequency wave produced lbywsaid discriminator meansWhich attenuates said audio frequencyl wave and circuit portions which provide a lowl impedance path `for 'the direct current voltagesl producedby said discriminator means in4 response toy said frequency shift' of saidca'rrier wave so. that said direct current voltagesblock said audio'amplier means, saidterminal--mean's including a circuit coupled Vto said audio amplifier means which provides a calling/.signalfin response -to the: blocking of said amplier means.

9. .A :dial Vtelephone systemincluding l inl combination, `irstand second terminal units,trans mittingzmeans and. receiving meanscouple'd'to eachiof: said=`terminal units with said transmitting means ofrsaid rst-terrninal unitfcommunicating with said receiving means of saidsecond terminal\"'unit and said transmitting means i of said :second terminal unit communicatingwith said receiving meansof said first, terminal-unit, said rstterminal means selectivelyY applying.` an audio wave and'dial pulses in the form of1dire'ct current signals recurring at a frequency of lthe order of twenty ycycles per second `to said transmitting means connected thereto, said transmitting means including means for producingla carrier wave and means for frequency modulating said carrier `wave by said 4audio waveand `for 'shifting' the frequency of said carrier wave in response to said ydirect current signals, said receiving means including discriminator means, audio amplifier means, and a coupling circuit therebetweemsaid discriminator means providing afvoltage vvarying in accordance with the deviation'of the received carrier Wave from the center frequency thereof, said'discriminator voltage corresponding tovsaid audio frequency waves and torsaid direct current signals applied tosaid modulating means, said coupling circuit including circuit portions providing a path for Ithe Aaudio frequency wave produced' by said vdiscriminator means which attenuate said audio lfrequency Wave and circuit portions which provide a low impedance pathwforthe receivingdirect current voltages produced by said discriminator means in response to frequency shift'ofsaidcarrier wave so that said direct -current lvoltages block said audio -amplier means,` said yterminal 13 means including a circuit coupled to said audio amplifier means Which provides a signal in response to the blocking of said amplifier means.

10. A dial telephone system including in combination, first and second terminal units, transmitting means and receiving means connected to each of said terminal units with said transmitting means of said first terminal unit communicating With said receiving means of said second terminal unit and said transmitting means of said second terminal unit communicating With said receiving means of said first terminal unit, each of said transmitting means including means for producing a carrier Wave and means for frequency modulating said carrier wave by an audio frequency wave and for shifting the frequency of said carrier Wave in response to a direct current signal, each of said receiving means including means for demodulating the received frequency modulating carrier wave and having an output stage which amplies audio frequency Waves derived thereby and which is blocked in response to a shift of the carrier Wave, said first terminal unit including means for selectively applying an audio frequency wave and dial pulses in the form of recurring direct current voltages to said transmitting means connected thereto, said second terminal unit including a circuit coupled to said output stage of the receiver connected thereto to receive said audio frequency Wave from said rst terminal unit and to provide signal pulses in response to the blocking of said output stage by the dial pulses from said rst terminal unit, said second terminal unit including means for selectively applying an audio frequency Wave and a steady direct current calling signal to the transmitter connected thereto, and said rst terminal unit including a circuit coupled to said output stage of the receiver connected thereto to receive said audio frequency Wave from said second terminal unit and to provide a calling signal at said rst terminal unit in response to the blocking of said output stage by the direct current calling signal from said second terminal unit.

11. A dial telephone system including in combination, first and second terminal units, transmitting means and receiving means connected to each of said terminal units with said transmitting means of said nrst terminal unit communicating with said receiving means of said f second terminal unit and said transmitting means of said second terminal unit communicating with said receiving means of said first terminal unit, each of said transmitting means including means for producing a carrier wave and means for frequency modulating said carrier wave by an alternating current signal and for shifting the frequency of said carrier Wave in response to a direct current signal, each of said receiving means including means for deriving signals from the received frequency modulating carrier Wave and having an output stage which amplies audio Waves derived thereby and which is blocked in response to a shifted carrier wave, said first terminal unit including means for applying dial pulses in the form of recurring direct current signals to said transmitting means connected thereto to intermittently shift the frequency thereof, said second terminal units including a circuit coupled to said output stage of the receiver connected thereto to provide signal pulses in response to the intermittent blocking of said output stage, said second terminal unit including means for applying a steady direct current calling signal to the transmitter connected thereto to aesassa shift the frequency thereof, and said rst terminal unit including a circuit coupled to said output stage of the receiver connected thereto and providing a calling signal in response to the blocking of said output stage by the calling signal from said second terminal unit.

12. A dial telephone system including in combination, first and second terminal units, transmitting means and receiving means coupled to each of said terminal units and intercommunieating with each other, each of said transmitting means including means for producing a carrier Wave and means for frequency modulating said carrier Wave by an audio frequency Wave and for shifting the frequency of said carrier Wave in response to a direct current signal, each of said receiving means including means: for demodulating the received frequency modulating carrier wave, an output stage and a circuit for interconnecting the same which attenuates the audio frequency Waves and which applies direct current signals derived from the shifted carrier Wave Without attenuation to thereby block said output stage, said rst terminal unit including means for selectively applying an audio wave and dial pulses in the form of recurring direct current voltages to said transmitting means connected thereto, said second terminal unit including a circuit coupled to said output stage of the receiver thereof to receive said audio Wave and to provide signal pulses in response to the blocking of said output stage, said second terminal unit including means for selectively providing an audio wave and a steady direct current calling signal to the transmitter connected thereto, and said rst terminal unit including a circuit coupled to said output stage of the receiver connected thereto to receive said audio Wave and to provide a calling signal in response to the blocking of said output stage.

13. A communication system for sequentially transmitting signal waves and control voltages including in combination, transmitting means including means for producing a carrier Wave and means for frequency modulating the same in response to the application of a voltage thereto, said transmitting means including an input circuit having amplifying means for applying an alternating current signal Wave to said modulating means and having attenuating means for applying direct current control voltage to said modulating means to shift the'frequency of said carrier Wave, and receiving means for receiving said carrier Wave, said receiving means including discriminator means, output circuit means, and a coupling circuit coupling said output circuit means to said discriminator means, said discriminator means providing a voltage varying in accordance with the deviation of said carrier Wave from the center frequency thereof, said coupling circuit attenuating alternating current voltages produced by said discriminator means in response to modulation of said carrier Wave by said signal wave and applying the same to said output circuit means, said coupling circuit applying direct current voltages produced by said discriminator means in response to said frequency shift of said carrier Wave to said output circuit means, said output circuit means having a portion thereof blocked by said direct current voltage to produce control voltages so that both said signal Wave and said control voltages are reproduced in said output circuit means.

14. A communication system including in combination, transmitting means including means for i producing, ias carriernwave; fimeansfor; :frequency modulating V,said carrier wave: in rresponse tothe application fofasignal voltages. thereto, .and an input Lcircuitahaving circuit portions forming ar fnrstl path, for, :applyingiaudio frequency Waves to said modulating means fand having circuit portions forming a-secondpath for applyingfdirect)currentsi'gnals to saidmodulating. means at a-reduced level to shift theirequency of1 said carrier fivave, and Ireceiving means for receiving saidycarrierfwaye, said-receiving meansincluding discriminator.means,output circuit means, and a coupling.circuity interconnecting said discriminator, imeans ,and saidfontputcircuit means, Vsaid discriminator means providinga voltagevarying in accordance;Withttheederivation of said carrier Wave from f the-- center v frequency thereof and; reproducing,saidfaudio'ffrequency waves :and said directcurrentl signals applied to said modulating means, said k.coupling .circuit `including circuit portions vproviding -a-,patli :for said reproduced audio .-frequency. :Wav-e,y .produced by; said discriminator means, Kand .circuit portions providing a lowximpedance epatnicr reproducedsteady and intermittent directfcurrent voltages yproduced by said discriminator `means .inresponse to frequencyfshift of-,saidcarrier-vvave, said output `circuit means ,amplifying said Yreproduced audio frequency-Waves and producing `control voltages in responseftotthe reproduceddirect current voltages.

15. vA- communication system including. in combination, vterminal means, tranmitting means and receivingmeans coupled to said terminal means, said kterminal .means selectively applying an audio Wave and fadirect currentsignalling -potential to said vvtransmitting means,saiditransmitting means including means .forproducing a carrier Wave `and means forfrequency modulating saidcarrier .Wave by said audio wave and forshifting the frequency of saidcarrier Wave in response to said direct current lpotentiahsaid ,receiving means demodulating thev carrier Wave received thereby to derive said audio wavetherefromand to provide a direct currentvoltagein response to frequency shift of the received carrier wave, said recevingmeans having an output stagavvhich amplies the recovered audiowaveandapplies, the vsame to said terminal means, said output stage. including a. portion which is Iblocked by` said `direct current voltage to produce a direct,currentsignalling potential for said 'terminal means.

16. A ipartyline, telephone system operating 'over a radio channel including in combination, Aa terminal unit and transmitting means and receiving meanscoupled to said terminal unit, said `terminal-unit including :means for selectively energizing said `transmitting ,and said receiving means and for selectively applyingan'audio Wave and a--direct lc urrentsignalling `potential to said transmitting --means 'when said transmitting means is'energized, saidtransmitting means including means for producing a carrier Wave and means for frequency ,modulating said carrier Wave by. said audio Wave and for shifting (the frequency of said 'carrier Wave in response to the application offvk said' direct current -signalling potential thereto,.said, receiving means vdemodulating ,the vfrequency modulated :carrier Wave received thereby to derive said audio ywave theredrom and tofprovide la direct current voltage in ,-responsevto frequencyshift of the receivedcarrier Wave, said receiving means-having an out- .rputsstagefwhich Afarnpliiies,the recovered audio WaveA and t including a :portion zwhich. Ais blocked inl response ,-Hto said-dir.ect :current voltage, :said terminal'unitl including circuit means coupled to said outputstageiwhich provides a signal inrespcnse to the blocking of said output stage.

17.-,gIn a-frequency lmodulation communication system i/vherein a carrierevfave is sequentallyrequency modulatedv by vaudio frequency Waves, and :shifted in. frequency yto provide' control functions, receiving means for lreceiving the carrier Wave .including -in combination, discriminator means, output circuit means including audio amplifier means, and a coupling, circuit connected between said 'discrimina-tor means and said output circuit means, saiddicriininator means. providing a Y voltage-varyingy in accordance with .the deviation offsaidgcarrier-wave from the center frequency thereof, said ,discriminator producing a voltagecorresponding to said audio frequency Wave in response to trequencymodulation of said carrier wave yandproducing a direct current voltage in responseto arshitt-of the .frequencytof saidcarrierwave, said coupling circuit including circuit portions providing a nrst-path for audio frequency wavesI vproduced by said discriminator means Vwhich attenuates the same and a second loW impedanceipathfor steady and intermittent direct current voltages produced by said discriminator means, in response to Yfrequency shift of said carrier wave, said output circuit means amplifying/,audio frequency-Waves `applied thereto and producing control volta-ges in response to said direct current voltages yappliedthereto.

v 18. In a frequency modulation communication system, transmitting means. for sequentially -handling alternating current signal Waves and direct current kcontrol voltages including in combination,.input terminala,oscillator` means -for producing a carrier'wave, modulating means coupled to said oscillator means for frequency modulating the same, an inputcircuitcoupling said,input terminalsto said modulating means, saidinput circuit having circuit `portions including an electron .discharge valve ,providing a vpath to,.said modulatingmeans for Aalternating current signal Wavesappliedtosaid input terminals, lsaid input ,circuitA havingcircuit portions providing a second path ktosaid ,modulating means for direct currentpontrol. voltages applied to said input terminals,y said modulating means providingfrequency deviation of said carrier `Wave, in response to said signal waves-and-shifting the frequency oisaidcarrierWavein response to said control voltages, said second circuit portion controlling the amplitude of .the direct-current control voltages appliedto said. modulating means sc that the frequency, of. said, .carrier Wave is shifted thereby to a greaterextentthan the deviation thereof produced. by the alternating current .signal Waves.

References Cited in the 'file of this patent UNITED STATES PATENTS Number Name Date 1,624,506 Pruden Apr. 12, 1927 2,263,633 Koch Nov. 25,-'11941 2,299,487 Moore Oct. 20, 1.942 2,315,050 vCrosby Mar. 30, 1943 2,333,992 FOX Nov. 9,1943 2,349,870 Koch `t/1ay;30,-194A 2,371,397 Koch Mar. 13, 1945 '2,383,908 ABowers Aug. 28, 1945 v.2,413,296 Deal etal.` Dec. 31,1946 2,457,434 Bartelinn 1 Dec. ,28,1948 

